Experimentally defining the safe and efficient, high pressure microwave plasma assisted CVD operating regime for single crystal diamond synthesis

The detailed experimental behavior of a microwave plasma assisted chemical vapor deposition (MPACVD) reactor operating within the high, 180-300 torr, pressure regime is presented. An experimental methodology is described that first defines the reactor operating field map and then enables, while operating at these high pressures, the determination of the efficient, safe and discharge stable diamond synthesis process window. Within this operating window discharge absorbed power densities of 300-1000 W/cm3 are achieved and high quality, single crystal diamond (SCD) synthesis rates of 20-75 µm/h are demonstrated. The influence of several input experimental variables including pressure, N2 concentration, CH4 percentage and substrate temperature on SCD deposition is explored. At a constant pressure of 240 torr, a high quality, high growth rate SCD synthesis window versus substrate temperature is experimentally identified between 1030 and 1250 C. When the input nitrogen impurity level is reduced below 10 ppm in the gas phase the quality of the synthesized diamond is of type IIa or better